Means and method for modulating fiber stock flow in papermaking headbox in response to paper sheet product parameters



DeC.l 15, 1970 D, A, BOSSEN ETAL 3,547,775

` MEANS AND METHOD FOR MODULATING FIBER STOCK FLOW IN PAPERMAKINCTHEADBOX IN RESPONSE TO PAPER SHEET PRODUCT PARAMETERS Filed April 29,1966 Dec. l5, 1970 D, A. BOSSEN ETAL 3,547,7'35

MEANS AND METHOD FOR MODULATING FIBER STOCK FLOW `IN PAPERMAKING HEADBOXIN RESPONSE TO PAPER SHEET PRODUCT PARAMETERS Filed April 29, 1966 2Sheets-Sheet 2 ro VAL vf: 52 7a 564, .4 661A/ QZ-[24,75 awr/Muff? DRYAJ/5 wr. WHO/P 41 otr. 'C ufr.

, 7 //.7 //0 I l JL/cf AND 3** 7`O Jl/CE CONTROL CONT/POL l/O JKITEHUnited States Patent Office 3,547,775 Patented Dec. 15, 1970 U.S. Cl.162--198 33 Claims ABSTRACT F THE DISCLOSURE A paper sheet formingapparatus and method wherein the fiber stock flowing to the sliceorifice of the headbox is modulated upstream of the orifice. The flowmay be suppressed by employing a flexible diaphragm which constricts thestock flowing to the orifice or by contacting the lower surface of thestock with a layer of liquid such as white water. These modulationsultimately affect the basis weight of the formed paper sheet. Further,the upper surface of the stock may be contacted with a layer of diluteliquid which then effects the moisture content of the formed papersheet. The flow consistency may be modulated by regulating the additionof either dilute liquid or fiber stock to the flowing `stock prior toexiting the orifice which ultimately affects the basis weight of theformed paper sheet. The flow modulation is controlled in response tocontroller means which include scanning moisture gauges and scanningbasis weight gauges.

This invention relates generally to product manufacturing apparatus, andmore particularly, to a method and apparatus for controlling the generaluniformity of product formed by adjustable members.

BACKGROUND FOR DESCRIPTION Quality control of industrial products havealways been difficult. Examples may be found in the manufacture of sheetproducts such as provided by a paper machine or a plastic extruderwherein weight uniformity, for example, of the sheet product is desired.

Some insight into the quality control problem can be gained by lirstexamining the apparatus commonly employed by paper manufacturers. Whileseveral different methods are used, one of the most common is theFourdrinier method by which an aqueous suspension of wood pulp fibers islaid over a traveling fine wire mat to form the paper sheet or web. Thefiber stock liows from a machine chest into a headbox from which itexits over a lip or through a slice opening or aperture extending acrossthe lateral extent of the wire mat. The size of the opening may beadjustable by slice screws to control the thickness dimension of theformed sheet. Water is removed from the sheet as it is carried along thewire mat. The sheet passes through press and dryer roll stands beforebeing wound up on a reel in substantially dry form.

BACKGROUND Many techniques have been employed to insure the manufactureof sheet of uniform weight per unit area or a basis weight. For example,individual automatic control of slice screw settings in accordance withthe measurements of a scanning radiation gauge is disclosed in U.S. Pat.3,000,438 issued Sept. 19, 1961 to F. M. Alexander, and assigned to thesame assignee as the present invention.

Both thickness and moisture content are simultaneously controlled by adryer temperature gauge as disclosed in U.S. Patent 1,936,225, issuedNov. 21, 1933 to A. E. Broughton. Thickness is controlled by alteringthe flow of stock before it enters the headbox with an adjustable flowof white water (diluted stock). A common conduit carries the white waterstock mixture to the paper Inachine where it is subsequently deliveredto the forming Wire or cylinder. Uniform moisture content is provided bychanging the amount of heat supplied to the dryer. With this type ofcontrol, there is an excessively long time lag between the point thestock flow is altered and the point it is deposited on the wire.

Other disclosures such as U.S. Patent 2,951,007, issued Aug. 30, 1960 toP. Lippke are concerned only with moisture control. This patentdiscloses the use of a scanning moisture gauge to control simultaneouslythe spraying of water laterally on a partially dried sheet and the sliceopening. The water spray may damage the sheet and may be ineffective formoisture control. The speed of slice adjustment is limited due to theinertia of the gearing system required to reduce the speed of theactuating motor making the control of basis weight or thicknessdifficult and unstable.

BRIEF DESCRIPTION OF THE INVENTION The present invention providesgenerally a method and means for quickly effecting a change in theweight per unit area of fibers deposited on the forming wire orcylinder. We modify or modulate the flow of fiber stock with a fluidbefore it exits the slice opening. In a preferred form, the flowmodification is hydrodynamic in nature and can be accomplished either byaltering the consistency 0f the stock just before it leaves the headboxor by suppressing or throttling the How thereof at this point in theprocess. Moreover, fluid modulation of flow can be provided at aplurality of points across the width of the machine to obtain uniformfiber weight per unit area of the formed sheet in the cross-sheetdirection, hereinafter referred to as profile, as well as in the machinedirection.

A liquid such as water, diluted fiber stock or white water, may be usedto provide the desired mixing or suppression. Usually, a source of whitewater is readily available and a conduit can supply a manifoldcommunicating with the interior of the headbox upstream from the slice.

In the flow consistency embodiment, the manifold exits are open to thestock flow and individual valves are installed to change the rate of owof white water into the headbox. The local consistency of fiber contentof the stock is altered by the mixing of the two flows occurring at eachmanifold exit. The modified stream then fiows out through the sliceopening and onto the wire.

In the flow suppression embodiment, at least two different methods maybe employed. The mechanical slice member is fixed and defines with thefloor of the headbox an aperture providing for a given cross-sectionalarea of flow normally occupied by the fibrous slurry. By employing flowdeflectors over the manifold exits, the liquid may be forced to flowgenerally in a layer adjacent to the stock and occupy a portion of theavailable headbox aperture cross-section. The layer flow thus providedserves to regulate the weight per unit area of the formed sheet.

The layer flow of liquid may be injected either at the top or at thebottom of the fiber slurry flow. Control exerted in the region of theupper ow permits regulation of the moisture content of the sheet sincethe liquid must drain through the sheet. Thickness control of the lowerflow permits regulation of the final sheet bone dry basis weight. Thelayer flow technique is distinguished from the stock mixing techniquedescribed above in the relative degree of flow turbulence resulting frominjection. The moisture profile control system enables more moisture tobe provided at the edges of the sheet than at the center to insure auniform cross-sheet moisture content after it is dried in a dryer havinga nonlinear drying rate.

In addition, rather than force the liquid into direct contact with thestock, it may be more advisable to confine the liquid flow in a closedhydraulic system wherein a force can be quickly transmitted by a liquidcolumn against a deformable elastic membrane positioned in the path ofthe slurry. The surface of the membrane cooperates with the edge of theslice member to establish a flow area of adjustable dimension. In thismanner, there is no commingling of the flows, but the fast response ofhydraulic actuation is provided nevertheless. By making the deformableelastic membrane permeable, some of the actuating liquid passes throughthe membrane and mixes with the stock producing a combined suppressionand dilution action. This suppressed flow control technique can beadvantageously applied to other product forming devices such as aplastics extruder die. In this embodiment, a deformable membranerestricts the flow of plastic directed out through the lips of the die.The thickness of the formed plastic sheet varies inversely with theextension of the membrane into the plastic flow.

In certain applications, our novel flow modulation techniques can beused in conjunction with a basis weight gauge positioned downstream fromthe headbox to measure and automatically control the weight per unitarea Of the formed sheet. More specically, a scanning gauge may be usedfor measuring the Weight per unit area of various cross-Sheet zones, thebasis weight or, in the alternative fiber content, of each zone beingdetermined by one of the several crossmachine fiow modulators. Theappropriate modulator is actuated to bring the basis weight of the sheetin its zone of control to the desired value. The modulator controlsignal may be developed after each zone is scanned. Alternatively, thegauge signal may be stored for purposes of a later correction in orderto eliminate any short term transient effects that might result fromimmediate zone-by-Zone control.

It should be noted that the basis weight of the sheet is equal to theproduct of the thickness and the density of the sheet. Therefore, theterms basis weight and thickness may be used interchangeably when thedensity is relatively constant. This assumption may not be true for somepaper-making processes. Since the modulators of the present inventionprimarily affect the fiber weight of the formed sheet, it may bepreferred to measure the dry weight per unit area of the sheet and basecontrol Accordingly, it is a primary object of the present invention toprovide a product manufacturing machine having a faster speed ofresponse than other devices of a similar nature.

It is another object of the present invention to provide an improvedbasis weight control system for a papermaking machine.

It is also an object of the present invention to provide a more stablepaper-making operation than heretofore possible.

It is yet another object vof the present invention to provide animproved method and apparatus for leveling both the moisture and thefiber weight profiles of a paper sheet product.

DESCRIPTION OF FIGURES FIG. l is a diagrammatic view of a paper-makingmachine comprising one preferred embodiment of the present invention;

FIG. 2 is a partial sectional view showing the construction of one typeof flow modulator for use in the machine shown in FIG. 1;

FIG. 3 is a partial sectional view of an alternative construction for aflow modulator;

FIG. 4 is a partial sectional view of another type of flow modulator;

FIG. 5 is a partial sectional view of an improved modulator for aplastic extruder;

FIG. 6 is a perspective view of a basis weight control systemconstructed in accordance with the present invention;

FIG. 7 is a partial sectional view, partially schematic, of a combinedbasis weight and moisture control system; and

FIG. 8 is a sectional view taken on the line 8 8 of FIG. 7.

DESCRIPTION O'F THE INVENTION With reference now to the drawings, andparticularly to FIG. l, the present invention is described in connectionwith a paper-making process but other types of product manufacturingprocesses may be regulated in a similar manner. A typical paper-makingline includes a machine chest 10 for storing the water-fiber slurry orstock that is deposited onto a traveling forming wire 12 to form thepaper sheet 14. The stock is frequently mixed by means of a valve 16with a flow of white water prior to the headbox 18. The mixture ispumped into the headbox 18 which has an exit slice lip 20 extendingacross the width of the forming wire 12. Excess water drains from thewire 12 and is later removed from the sheet 14 by rolls in a presssection 22 and a dryer section 24. A reel 26 winds up the dried papersheet.

It is desirable to produce a sheet having a uniform weight per unit areaor basis weight. To this end, mechanical slice members have heretoforebeen employed across the lip 2t) of the headbox and adjusted manually orautomatically up or down, depending on whether the sheet was runninglighter or heavier than desired. Motion was provided by a screwconnected to the slice member. A motor was coupled to the screw by meansof a reduction gearing arrangement. In general, this type of actuatorhas left much to be desired because of its sluggish operation. Backlashand inertia effects have made control of the slice member very difcult.Further, the amount of mechanical warpage is limited and excessivecorrective action can cause slice failure.

In an effort to increase the speed of response we have provided ahydraulic system which modulates the stock flow in the region of the lip20. Not only is the speed of response increased but the system alsorequires fewer moving components. The hydraulic system includes an exitflow modulator 30 coupled to a hydraulic actuator 32. A liquid supplyunit 34 may include pumping equipment to maintain in the conduit 36either a fixed volumetric flow rate or a given head or pressure. Theflow modulators coupling to the stock flow is illustrated by the dottedline 38 extending toward the lip 20 of the headbox.

Generally speaking, the modulator 30 affects the distribution of thefibers being deposited on the wire 12 thereby altering the weight perunit area of the formed sheet 14. The modulator 30 may affect the flowequally at all points across the face of the lip 20. Alternatively, itmay be desired to produce a sheet heavier in some crosssheet areas thanin others, or to otherwise increase the flexibility of thesystem, inwhich case, a plurality of individual modulators are provided, eachaffecting the flow across and through a small local region of the lip.The stock flow in the headbox 18 is modulated upstream from the lip 20at a point where the flow is relatively streamlined with little lateralmixing. The location of this point depends on the construction of theheadbox. Since the flow streamline improves the nearer one approachesthe lip 20, we have found it preferable to modulate in this region. Aconstant mass flow of fiber through each region produces a constantbasis weight zone extending downstream in the machine direction towardthe press and dryer sections 22 and 24. Several of these zones,sideby-size, occupy the width of the sheet 12 and determine the profileor variations in the value of a physical variable of the sheet such asbasis weight or moisture with distance across the sheet 14. A discussionof profile measurement and control will be taken up hereinafter; but,rst it is instructive to describe several types of preferred flowmodulators. For simplicity, these descriptions are conlined to a singlemodulator operative to vary the sheet weight of only one zone.

FLOW CONSISTENCY MODULATOR One type of modulator is shown in FIG. 2. Anenlarged view taken at a cross-section of the lip reveals a holey roll40 positioned between the floor 42 and the The purpose of thisembodiment is to alter the consistency of the stock stream 46 before itexits the lip opening 20a and is deposited onto the form wire 12. Thismay be accomplished by altering the flow in other streamline flowregions further upstream in the headbox 18. A change in consistencymeans, of course, that the mass flow of liber through the opening 20awill be altered. This alteration of ber mass flow is reflected by acorresponding change in the basis weight of the sheet being formed.Although many ways may be available to vary the stock consistency, oneof the most convenient is to mix liquid `with the slurry to dilute thesame. This procedure assumes that, with no liquid being added, the stockis suiiciently dense to provide the heaviest sheet weight desired.Liquid dilution of the stock decreases the sheet weight. It is, ofcourse, Within the scope of this invention to add liber to local ow ifthe foregoing assumption cannot be made.

Water or other liquid may be added to change the flow consistency. Theready availability of white water ma'kes this liquid most convenient.White water may be pumped through a conduit 48 that terminates in theinterior of theheadbox 18 preferably between the holey roll 40 and thelip opening 20a. The flow of white water, indicated by the singlecurvilinear arrows 50, commingles with the local stock flow 46. Anadjustable liquid flow regulator 52 may be provided in the conduit 48 tovary the amount of white water llowing per unit time into the headboxlip 20. The flow regulator S2 may be manually adjustable by means of aknob 54 to Vary the consistency of stock delivered to the forming wire12. For example, an increase in white water ow, lowers the stockconsistency and decreases the weight of the sheet 14. Conversely,throttling of the white water ow increases the basis Weight of thesheet. Automatic control of the white Water ow will be describedhereinafter.

FLOW SUPPRESSION MODULATOR EMBODIMENTS Another embodiment of modulatoralters the mass flow of stock from the lip 20 by suppressing the flowhydrodynamically. FIGS. 3 and 4 illustrate only lnwo of several forms ofsuppression. In either case, the total exit area of ow available to thelocal fiber stock flow 46 is throttled by movable diaphragm membersactuated by white water or other fluid. This stock flow exit area isproportional to the height of the opening indicated by the thicknessdimension tf of fiber slurry laid on the wire.

In FIG. 3, a valve such as a flexible stainless steel cover 56 ispositioned over the open end of the conduit 48. The rear of the cover 56is fastened to the floor 42 of the headbox 18 away from the lip opening20a. White water 50, owing into the headbox, strikes the steel valve 56deecting it upwardly in accordance with the pressure in the conduit 48.A laminar ow of white water 50 deflected by the valve 56 is providedbeneath the local stock flow 46 and occupies a portion of the total lipopening 20a proportional to the thickness t1 of the white water layer.

There is little, if any, change in the consistency of the slurry 46 inthis embodiment. The weight of the sheet 14 is increased by reducing themass flow of white Water owing into the headbox. The valve 56 lowers andpermits an increase in the flow of liber out through the lip opening20a. The underlying layer of white water quickly drains through the wire12 and is collected and recirculated. The remaining iibrous sheettravels on to be dried more completely.

Another flow suppression embodiment is shown in FIG. 4. Here adeformable elastic membrane 60 completely encloses the end of conduit48. No white water is pei'- mitted to ow but a force is conveyed by theenclosed liquid column and directed against the membrane 60 to projectmore or less of its outer surface into the path of the fiber stock 46flowing toward the lip opening 20a. A pressure regulator 62 is madeadjustable to vary the head or pressure of the liquid column provided inthe closed system.

This technique of flow control may also be applied to a plasticextruder. FIG. 5 shows a portion of an extruder housing 41 containing asupply of plastic material 43. Normally, the plastic material 43 isforced out of the extruder housing 41 through a pair of die members 45aand 4511. The die may be either linear to provide a at sheet of plasticor circular as commonly employed on blown film lines. In either case,the die is normally adjustable at sections along its length by means ofmechanical screws (not shown) capable of altering the gap thickness atthe lip 47 of the die. This atfects the thickness of the extrudedproduct. A better description may be found in an article by H. E.Sponaugle entitled Automatic Profile Gauge Control reported at vol. 19,No. 6, June 1963 of the Society of Plastics Engineers Journal.

We have found it preferable to employ a movable diaphragm 49 between thelip 47 and the main body 41 of the extruder to change the thickness ofthe extruded plastic product. A fluid pressure system 51 may be used toprovide a flow of fluid against the underside of the diaphragm 49 toforce it upwardly against the flow of plastic. The diaphragm 49 may becarried in a pair of slots 53 provided in one of the die members 45h. Avalve 55 controls the fluid pressure and thus the thickness of theextruded product.

A plurality of diaphragms can be provided along the length of the die tocontrol the profile of the extruded sheet product. In this case, a valve55 is connected between the fluid pressure system 51 and each diaphragmand adjusted in accordance with the zone control techniques describedhereinabove.

Other diaphragm constructions may be employed to provide the desiredresult. In certain types of extruders it may be more desirable toeliminate the diaphragm member and direct a ow of readily vaporizableuid against the flow of plastic to restrict the same in a manner similarto that described above in reference to the papermaking apparatus.

In the operation of this embodiment, to decrease the basis weight of theformed sheet, an increase in white water pressure extends the membrane60 upwardly, thereby constricting the stock ow from the lip opening 20a.The ber thickness tf decreases causing a reduction in the weight perunit area of the sheet 14. A basic weight increase can be accomplishedby a reduction of the pressure in the conduit 48. It will be apparent tothose skilled in the art that many alternatives of this embodiment arepossible. For example, membranes of various materials, sizes andmounting position may be tried, depending on the weight and character ofsheet being produced. For example, semi-porous membranes may be used,permitting a combination of both the stock consistency and the stocksuppression techniques of the invention. In addition, other variationsof the hydraulic actuating system may be made to improve the operationof the system.

Regardless of which type of modulator is selected, it is apparent that afast mode of weight control is available due to the employment of ahydraulic actuating system. Any of the modulators described above can beadvantageously combined with sheet Iweight gauging apparatus to providean improved automatic control system. Such a system is described in thefollowing section.

IMPROVED FIBER WIEGHT CONTROL SYSTEM With reference now to FIG. 6,several modulators can be positioned side-by-side across the width ofthe headbox 18 to produce a sheet 14 having a predetermined ber weightprofile; frequently ber weight per unit area is termed bone dry basisweight. Six modulators are shown for purposes of illustration. Eachmodulator controls the fiber `weight per unit area, i.e., bone dry basisweight, in one of the six zones #1-#6 defined by the dotted linesextending in the machine direction down the sheet 14. Hereinafterapparatus associated with a particular zone will be identied with asubscript numeral indicative of that zone. A manifold piping arrangement64 may be employed to convey the white Water to the several localcross-sheet regions of the lip 20. The ow modulators are showncommunicating with the upper surface 44 of the lip 20 for convenience ofillustration. A separate -valve 661-666 serves to regulate the mass flowof white water into each local lip region. Other ilow regulating devicesmay also be suitable for this purpose.

In order to derive control signals suitable for actuating the valves661-666, a traversing gauge 70 is employed to scan the sheet 14laterally and provide on line 72 a signal proportional to the ber weightper unit area of the portion of the sheet being scanned. A measuringcircuit 74 amplities this signal and transmits it to an error signaldetector 76. Detector 76 develops a signal whenever the measured weightand the desired weight differ. Controller 78 causes actuation of anappropriate one of a bank of motors 80 each coupled to one of thelvalves 66 by means of an actuator selector unit 82. A scanningprogrammer 84 causes the gauge 70 to scan across the sheet 14 anddemands from the actuator selector 82 that the controller 78 be coupledto the appropriate motor in the bank 80 to insure that 'weight controlis exerted on the zone being measured. The cooperation between theprogrammer 84 and the guage 70 and the actuator selector 82 is indicatedby the heavy dotted line 86. A more detailed description of theconstruction of some of the units briey described above may be found inthe aforementioned patent to Alexander. Alternatively, the modulatorscan be controlled simultaneously by changing the programming andselection functions of units 84 and 82 respectively.

The gauge 70 may include any of the known sensors sensitive to basisweight such as those operating on the radiation absorption principle.U.S. Pat. 2,790,945, issued to H. R. Chope and assigned to total thesame assignee as the present invention describes a gauge of this type.Since the sheet 14 is eventually dried to a very low moisture content,it is usually desirable to maintain uniformity of the bone dry weight ofthe sheet. A total sheet weight measurement may have to be compensatedfor moisture (if it rvaries signicantly) to compute the dry weight andpermit more accurate control of the fiber content by our improvedmodulators. It is appreciated that the total sheet basis weight isproportional to the dry basis `weight thereof only when the moisturecontent of the sheet remains invariant. Gauge 70 would includepreferably both a moisture sensor and a basis weight sensor andinstrumentation providing for the moisture compensation of a total basisweight signal would be provided in measuring circuit 74. Circuit 74`would deliver an amplified signal proportional to the dry weight perunit area or dry basis weight of the sheet region being scanned.

The mounting location of the gauge is not critical; however, it ispreferred to position the gauge as near as possible to the headbox 18 toshorten the time lag between the point of control and the point ofmeasurement. Measurement of the sheet 14 as soon as possible after itleaves the forming wire 12 would provide a time lag of only a fewseconds at the most. Of course, measurement after the dryer section 24would eliminate the need for moisture compensation but the excessivelylong transport time may nullify the advantages afforded by themodulators quick response.

Since the gauge will measure an area of sheet substantially smaller thanthe width of the cross sheet zones, provision may be made to average theweight of the sheet across each zone. `Electrical integrators similar tothose described in the Alexander patent, supra, may be employed for thispurpose.

This system operates in the following manner. The gauge 70 scans acrossZone #l and the dry `weight of this area of the sheet 14 is computed.The gauge signal may be stored while the entire sheet is scanned. Thestored signal may be drawn from storage and used to provide the desiredzone-by-zone prole control. Alternatively, control for a given zone maybe effected immediately after that area of the sheet is measured. If thecomputed dry weight is larger than it should be, controller 78 energizesmotor 80, for a period of time proportional to the weight error. Valve661 is actuated to increase the ow of white water into the left-handedge of the slice lip 20. Accordingly, a reduction in sheet weight inany zone lwill be accompanied by an increase in the ilow of white waterinto the region of the lip associated with the zone. Successivemeasurement and control of sheet zone weight enables the fiber weightprole of the sheet to be leveled. It also permits contouring of theprole if it is desired to have a sheet lighter or heavier in the centerthan near the edges.

COMBINED MOISTURE AND FIBER WEIGHT CONTROL SYSTEM The present inventionprovides not only for ber prole weight control but also for moistureprofile control of the sheet 14. This is of great benet in view of thenonlinear drying characteristics of most dryer sections. Dryerscharacteristically remove more water from the edges of the sheet thannear the center. This means that the dried sheet will not have a uniformcross-sheet moisture content. Moreover, the sheet may be damaged byoverdrying the edges in attempting to eliminate the wet center. Anattempt has been made to correct this without success by skewing thepress rolls.

We precondition the sheet by supplying white water to the upper surfaceof the fiber stock flowing out through the slice opening 20a. A greaterow of white Water is provided at the edges of the slice opening than atthe center of the sheet. The added white water eventually drains throughthe sheet, but the center is left with a lower moisture content than theedges. After passing through the dryer 24, the sheet emerges with alevel moisture prole.

FIGS. 7 and 8 illustrate this novel method of sheet moisture control.The headbox construction is similar to that described above `with theexception that a vertically adjustable slice member is shown definingthe exit llow area with the floor of the headbox 18 from which the fiberstock flows in a sheet layer 92. The flow of white water through aconduit 94 communicating `with the roof of the headbox lip 20 iscontrolled by an adjustable valve 96. The water is deposited on top ofthe liber stock in a layer 98, the thickness of which decreases withdistance from the headbox because of drainage through the fiber stocklayer 92.

A moisture gauge 100 measures the moisture content of the sheet beforeit enters the dryer section 24. The type of moisture gauge used is notcritical. A moisture measurement and control unit 102 may be used toactuate the valve 96. i

Several valves may be provided across the width of the headbox lip toprovide the desired moisture profile illustrated in FIG. 8. The desiredmoisture prole of the sheet 14 prior to entering the dryer 24 isindicated by the crowned liquid layer 98. The illustration isdiagrammatic and is not necessarily the distribution of white water andfiber actually occurring in the sheet 14 at this point in the process.To obtain the nonlinear moisture profile shown in FIG. 8, the controlunit 102 works against a dilferent desired or target moisture contentfor each zone #1-#6. For example, the target moisture for zone #2 may beseveral percent lower than that for zone #l and yet several percenthigher than that set for zone #3 near the center of the sheet 14. Inmost cases, the prole will be symmetrical about the center of the sheetand the targets for zones #4, #5 and #6 may be substantially the samevalues set for zones #3, #'2, and #1, respectively.

To accommodate this prole control, the moisture gauge 100 must bescanned across the sheet unless the moisture variations are proportionalat al1 points across the machine, in which case, a single pointmeasurement will be representative. Valve control is coordinated withthe scanning of the moisture gauge 100 in a manner similar to thatdescribed above in connection with FIG. 6 to insure that moisturecontrol is exerted on the zone being measured. Of course, simultaneousvalve operation is an alternative mode of operation as in the case ofbone dry basis Weight control.

Concomitant bone dry basis weight control may be employed by positioninga ber content measuring gauge 104 after the dryer 24. Little, if any,moisture compensation of the gauge 104 is required when it is locatedadjacent to the dried sheet. A bone dry basis weight modulator 108utilizes the output signal from the gauge 104 and control system 106 tovary the stock consistency of the ow exiting the lip 20. Of course, thesuppression methods of weight modulation described hereinabove also maybe employed with substantially equal utility.

A coarse adjustment of bone dry basis weight may be provided by slicecontrol unit 110 energizing a motor 112 mechanically coupled to theslice member 90 (see the Alexander patent, supra). This alternative isdesirable should a correction be called for that may be beyond thecapability of the hydraulic modulator 108. It may be apparent that anyadjustment of either the slice member 90 or the flow consistency mayalter the moisture content of the sheet 14 as well as the dry ber weightper unit area. Therefore, the cooperation of the two variable controlsystems, viz. bone dry basis weight and moisture, is evident and bothare required for the most economical return derivable from profileleveling.

Our system for measuring and controlling the dry weight and moisturesimultaneously may be provided for other processes and by equipmentother than that disclosed hereinabove. For example, dry weight may becontrolled by a slice adjustment alone or by regulation of a stockdilution valve located upstream from the headbox. Product moisturecontent may be controlled by spraying water directly on the product invarying amounts or by regulating the humidity of the environment inwhich the product is produced.

SUMMARY The present invention provides a new method of papermakingwhereby the bone dry basis weight and moisture of the sheet product areautomatically regulated to reduce significantly the amount ofundesirable footage product and to permit control within narrow limits.This results from the use of fast-acting hydraulic actuators modulatingthe flow of liber stock as it is deposited onto the forming member,whether it be a wire, cylinder or other type. In addition, the presentinvention also provides a moisture profile control system to correct forthe non-linear drying rates prevailing in different lateral regions ofthe dryer section. Simultaneous measurement and control of both themoisture and the ber weight is another important feature of ourinvention.

Although certain specic embodiments of the invention have been shown anddescribed herein, many modifications may be made thereto withoutdeparting from the true spirit and scope of the invention as set forthin the appended claims.

I claim:

1. A method of controlling the formation of a fibrous sheet productderived in response to a fibrous slurry emerging from a headbox outletand being fed to a drying Wire, said slurry having a bottom, horizontalsurface as it emerges from the outlet, said headbox having a floor,comprising feeding a liquid dilute relative to the slurry along thefloor into substantial contact with the bottom surface of the slurry sothat the slurry as it emerges from the outlet and While it is on atleast a portion of the wire is bounded on said surface by the diluteliquid, measuring a parameter of the product affected by the diluteliquid, deriving an error indication for the parameter in response tothe measured value and a target value, and controlling ow of the diluteliquid in response to the error indication.

2. The method of claim 1 further including the steps of measuring themoisture content of the formed sheet product and controlling the iiow ofthe dilute liquid to the upper surface of the slurry in response to themeasured moisture content to maintain a substantially predeterminedmoisture content in the formed sheet product.

3. The method of claim 1 further including the steps of measuring thefiber content of the formed sheet product, and controlling the flow of'the dilute liquid to the lower surface of the slurry in response to theiiber content measurement to maintain the iiber content substantially ata predetermined value.

4. The method of claim 1 wherein the slurry has an upper surface as itemerges from the outlet and further including the steps of measuring themoisture and fiber content of the formed sheet product, and controllingthe liovv of the dilute liquid to the upper and lower surfaces of theslurry in response to the moisture and ber content measurements,respectively, so that the formed sheet product has a predeterminedmoisture and fiber content.

5. A method of controlling the formation of a brous sheet productderived in response to a fibrous slurry emerging from a headbox outlet,the headbox having a floor and including a deflocculating roller forslurry iiowing to the outlet, comprising modulating the flow of localslurry to said outlet by feeding a liquid dilute relative to the slurryalong the headbox oor into contact with the slurry at a locationimmediately upstream of the outlet and downstream of the roller tocontrol the amount of fiber passing through the outlet, said llow beingmodulated by bringing said dilute liquid into substantial contact withonly the bottom surface of the slurry, directing said dilute liquidtoward the slice to control the mass iiow rate of the slurry throughsaid outlet, measuring a parameter of the product affected by the diluteliquid, deriving an error indication for the parameter in response tothe measured value and a target value, and controlling flow modulationin response to the error indication` 6. A method of controlling thformation of a fibrous sheet product derived in response to a librousslurry emerging from a headbox slice opening, the headbox having adeilocculating roller feeding slurry to the opening,

comprising modulating the flow of local slurry to said slice opening byfeeding a liquid dilute relative to the slurry into contact with theslurry at a location immediately upstream of the opening and downstreamof the roller to control the amount of fiber per unit volume of liquidpassing through the slice opening, measuring the dry weight of the sheetproduct, deriving an error indication between a target Value for dryweight and measured dry weight, and controlling the ow of the diluteliquid in response to the dry weight error indication to achieve adesired sheet liber content.

7. The method of claim 6 wherein said slurry has a lower, horizontalboundry layer and said ow is modulated by varying the mass flow rate ofslurry passing through the slice by bringing said dilute liquid intosubstantial contact with only said boundry layer of the slurry anddirecting said dilute liquid towards the slice.

8. The method of claim 6 wherein said slurry has a lower horizontalboundry layer and said flow is modulated by varying the mass flow rateof slurry passing through the slice by bringing said dilute liquid intosubstantial contact with only a surface of the slurry and directing saiddilute liquid towards the slice, said measuring step including derivinga measurement of the dry weight in each of a plurality of zones acrossthe width of the sheet, said error deriving step including deriving anerror indication between a target value and measured dry weight in eachof the zones, and said modulating step including responding to the errorindication in each of the zones to control an actuator for the diluteliquid in each of a plurality of cross-sheet regions corresponding withthe cross-sheet zones to achieve a desired sheet dry weight in each oflthe regions.

9. The method of claim 6 wherein the modulating step includes varyingthe consistency of the slurry passing through the slice by comminglingthe dilute liquid with the slurry.

1t). The method of claim 6 wherein the modulating step includes varyingthe consistency of the slurry passing through the slice by comminglingthe dilute liquid with the slurry, said measuring step includingderiving a measurement of the dry weight in each of a plurality of zonesacross the Width of the sheet, said error deriving step includingderiving an error indication between a target value and measured dryweight in each of the zones, and said modulating step includingresponding to the error indication in each of the zones to control anactuator for the dilute liquid in each of a plurality of crosssheetregions corresponding with the cross-sheet zones to achieve the targetdry weight in each of the zones.

11. The method of claim 6 wherein said measuring step includes derivinga measurement of the dry weight in each of a plurality of-zones acrossthe width of the sheet, said error deriving step including deriving anerror indication between a target value and measured dry weight in eachof the zones, and said modulating step includes responding to the errorindication in each of the zones to control an actuator for the diluteliquid in each of a plurality of cross-sheet regons corresponding withthe cross-sheet zones to achieve the target dry weight in each of thezones.

12. The method of controlling the moisture content of a paper sheetformed by depositing a slurry of ber stock owing through an aperture ofa headbox onto a moving forming member, said headbox including adeocculating roller comprising the steps of: measuring the moisturecontent of said formed sheet, responding to the measured moisturecontent and a moisture target Value to derive a moisture errorindication, and injecting a flow of a liquid dilute relative to theslurry between the roller and aperture into contact with the uppersurface of said slurry while the slurry is within the headbox, andcontrolling the flow rate of lthe dilute liquid in response to themoisture error indication to maintain the measured moisture content ofsaid sheet at the target value.

13. The method of claim 12 which further includes the step ofselectively controlling said liquid flow at each of several regionsacross said aperture to provide a sheet having a predetermined moistureprofile characteristic.

14. The method of controlling the uniformity of a paper sheet formed bydepositing ber stock flowing through an aperture onto a moving formingmember, said stock flowing through the aperture having an upper surface,comprising the steps of measuring the moisture content of the sheet,responding to measure moisture content and a moisture target value toderive a moisture error indication, controlling the injection flow of adilute liquid adjacent the upper surface of said iber stock flow priorto the formation of the sheet in response to the moisture errorindication to maintain the moisture content of said sheet at themoisture target value,

measuring the bone dry basis weight of the sheet, re-

sponding to measured bone dry basis weight and a bone dry basis weighttarget value to derive a bone dry basis weight error indication, andcontrolling the mixing of a liquid with said stock flow in response tothe bone dry basis weight error indication to maintain the consistencyof said deposited fiber stock at the bone dry basis weight target.

1S. Control apparatus for a papermaking machine, comprising:

a headbox for storing fiber stock and including a slice lip opening fordelivering a local ilow of said stock onto a moving sheet-forming wireand a roll rotatably mounted in the path of said stock flowing towardsaid lip opening to prevent flocculation of said ber stock,

a dryer section having a non-linear cross-sheet drying characteristicwhereby certain cross-sheet zones of said sheet are dried to a greaterextent than others, and

a plurality of means positioned across said lip opening and between saidlip opening and said rotatable roll for modulating the moisture contentof said stock exiting said lip opening in each of said zones,comprising:

separa-te means for each of said zones feeding a source of dilute stockof controllable amounts on to different cross-sheet zones of the uppersurface of said stock flow to change the moisture content of said sheetin each of said zones, and

means for controlling each of said modulating means to provide a sheethaving a moisture prole characteristic inversely related to thecross-sheet drying characteristic of said dryer section to provide adried sheet having a uniform moisture profile.

16. Control apparatus as set forth in claim 15 which further includesmeans for simultaneously hydrodynamically controlling the local flow ofsaid fiber stock to provide a sheet having a uniform bone dry basisweight.

17. Control apparatus as set forth in claim 15 which further includesgauge means for measuring the moisture content of said sheet to generatea control signal for said controlling means.

18. Control apparatus for a papermaking machine including a headbox forstoring a slurry of ber stock and including aperture means fordelivering a local flow of said slurry onto a moving sheet-forming wireand a roll rotatably mounted in the path of said slurry flowing towardsaid aperture means to prevent flocculation of said liber stock, saidslurry having an upper surface while in the headbox, a dryer sectionhaving a nonlinear crosssheet drying characteristic whereby certaincross-sheet zones of said sheet are dried to a greater extent thanothers, the improvement comprising:

means positioned between said roll and aperture means for feeding aliquid dilute relative to the slurry onto the upper surface of theslurry to control the moisture content across said sheet to provide saidsheet entering said dryer section with a moisture profile characteristicinversely related to said cross-sheet drying characteristic of saiddryer section, said liquid feeding means including different actuatorsfor the different cross-sheet zones, and

means controlling said actuators to enable the inverse moisture profileto be attained.

19. Control apparatus for a papermaking machine,

comprising:

a headbox for storing fibrous stock including a slice lip opening fordelivering a local flow of said stock onto a moving sheet-forming wireat least as wide as said slice lip opening and a rotatable memberpositioned in the path of said stock flowing to said slice lip openingto prevent flocculation of said slurry fibers,

a plurality of stock flow modulating means positioned 'between saidslice lip opening and said rotatable member and spaced across the widthof said opening to vary the consistency of said stock flow at each ofseveral local regions, said modulating means including:

a source of diluted stock and means for mixing a controllable proportionof said diluted stock with said local flow of fibrous stock.

gauge means scanning across said sheet formed by said wire to provide acontrol signal indicative of the variations in the dry weight of saidsheet in each `cross-sheet zone corresponding to one of said local stockow regions, and

control means responsive to said control signal for actuating each ofsaid valve means. to vary the fiber content per unit area of saidscanned cross-sheet zone.

20. In an apparatus for controlling the formation of.'

a fibrous sheet product, a headbox feeding a slurry of fibrous materialto a slice opening, said headbox having a Iiioor and including adefiocculating roller for slurry flowing to the outlet, means within theheadbox immediately upstream of the outlet and downstream of the rollerfor modulating the flow of local slurry to said slice opening to controlthe consistency of fiber in liquid passing through the slice opening,and a wire downstream of the outlet for receiving the slurry emergingfrom the outlet for enabling liquid to be removed from the emergingslurry, the slurry emerging from the outlet and received by the wirehaving a bottom surface, said modulating means including means forfeeding a liquid dilute relative to the slurry along the oor intosubstantial contact with the bottom surface of the slurry emerging fromthe outlet so that the slurry fed to the wire is bounded on said surfaceby said dilute liquid, means for measuring a parameter of the formedsheet product affected by the dilute liquid, means responsive to saidmeasuring means to a target value for the parameter for deriving anerror signal and means responsive to the error signal for controllingthe flow of the dilute liquid onto said surface to control the sheetparameter.

21. The apparatus of claim 20 further including means for measuring themoisture content of the formed sheet product and means responsive tosaid measuring means for controlling the flow of the dilute liquid tothe upper surface of the slurry.

22. The apparatus of claim 21 wherein a dryer is positioned downstreamof said wire, and said measuring means is positioned upstream of thedryer.

23. The apparatus of claim 20 further including means for measuring themoisture and fiber content of the formed sheet product, and meansresponsive to the measured moisture and fiber content for controllingthe ow of the dilute liquid to the upper and lower surfaces,respectively, of the slurry.

24. In an apparatus for controlling the formation of a fibrous sheetproduct, a headbox feeding a slurry of brous material to a sliceopening, said headbox having a deiiocculating roller, means within theheadbox immediately upstream of the slice and downstream of the rollerfor modulating the ow of local slurry to said slice opening to controlthe amount of fiber per unit volume of slurry passing through theopening, said modulating means including means for feeding a liquiddilute relative to the slurry into contact with the slurry, means formeasuring the bone dry basis weight of the sheet product, meansresponsive to the bone dry basis weight measuring means and to a targetValue for bone dry basis weight of the sheet product for deriving a bonedry basis weight error signal, and actuator means responsive to the bonedry basis weight for controlling the flow of the dilute liquid to themodulating means.

2S. The apparatus of claim 24 wherein said slurry has a bottom surfaceIand said modulating means includes means for varying the mass flow rateof slurry passing through the slice by bringing said dilute liquid intosubstantial contact with only the bottom surface of the slurry and fordirecting said dilute liquid towards the slice opening.

26. The apparatus of claim 24 wherein said modulating means includesmeans for varying the mass flow rate of slurry passing through the sliceby bringing said dilute liquid into substantial contact with only asurface of the slurry and for directing said dilute liquid towards theslice opening, said measuring means including means for deriving ameasurement of the bone dry basis weight in each of a plurality of zonesacross the width of the sheet, and said modulating means beingresponsive to an error signal for each of the zones derived in responseto the measurement in each of the zones and a target value to vary thebone dry basis weight in each of a plurality of cross-sheet regionscorresponding with the cross-sheet zones.

27. The apparatus of claim 24 wherein said modulating means includesmeans for commingling the dilute liquid with the slurry to control thefiber consistency of the slurry passing through the slice.

28. The `apparatus of claim 24 wherein said modulating means includesmeans for varying the mass flow rate of slurry passing through the sliceby bringing said dilute liquid into substantial contact with only asurface of the slurry and for directing said dilute liquid towards theslice opening, said measuring means including means for deriving ameasurement of the bone dry basis weight in each of a plurality of zonesacross the width of the sheet, and said modulating means beingresponsive to an error signal for each of the zones derived in responseto the measurement in each of the zones and a target value to vary thebone dry basis weight in each of a plurality of cross-sheet regionscorresponding with the cross-sheet zones.

29. The apparatus of claim 24 wherein said measuring means includesmeans for deriving a measurement of the bone dry basis weight in each ofa plurality of zones across the width of the sheet, and said modulatingmeans being responsive to an error signal for each of the zones derivedin response to the measurement in each of the zones to vary the bone drybasis weight in each of a plurality of cross-sheet regions correspondingwith the cross-sheet zones.

30. In an 'apparatus for controlling the formationV of a fibrous sheetproduct, a headbox having a deocculating roller feeding a slurry offibrous material to an outlet of the headbox, said headbox having afloor, said slurry having 'a bottom surface, and means within theheadbox immediately upstream of the outlet and downstream of the rollerfor modulating the flow of local slurry to said outlet to control theamount of fiber passing through the outlet, said modulating meansincluding conduit means having an orifice for feeding a liquid diluterelative to the l slurry along the headbox floor into contact with theslurry, said modulating means further including means for bringing saiddilute liquid into substantial contact With only the bottom surface ofthe slurry and for directing said dilute liquid towards the outlet tocontrol the mass fiow rate of the slurry passing through the outlet,gauge means for sensing the dry Iweight of the sheet, means responsiveto said gauge means and a target value for dry weight for deriving a dryWeight error signal, and means controlling said modulating means inresponse to the error signal.

31. Control apparatus for a fibrous product manufacturing machineincluding a headbox for storing fibrous stock and having flow aperturemeans providing for a ow of said fibrous stock onto a product formingwire, said stock flowing through the aperture having an upper surface,said apparatus comprising:

gauge means positioned adjacent and responsive to the moisture contentand basis 4Weight of said formed product to lprovide a first signalindicative of the moisture content of said formed product and a secondsignal indicative of the bone dry Weight of said formed product, meansresponsive to said first signal and a target value for moisture contentfor deriving a moisture eiror signal,

means responsive to said second signal and a target value for bone dryweight for deriving a bone dry basis Weight error signal, meansresponsive to said moisture error signal for injecting Water onto theupper surface of said fibrous stock flowing to said Wire to control themoisture content of said formed product so that it is substantiallyequal to the moisture target value, and

means responsive to said bone dry basis Weight error signal formodulating the local flow of said fiber stock in the region of saidaperture to control the bone dry basis Weight of said formed product sothat it is substantially equal to the bone dry basis weight targetvalue. 32. Control apparatus for papermaking machine including `aheadbox for storing fibrous stock and having an aperture from which saidstock llovvs onto a moving Wire to form a sheet, said apparatuscomprising:

first gauge means positioned adjacent said formed sheet to provide ameasurement signal proportional to the moisture content of said formedsheet,

second gauge means positioned adjacent to said formed sheet to provide ameasurement signal proportional to the dry IWeight per unit area of saidformed sheet, first controller means responsive to said moisturemeasurement signal and a target value for sheet moisture for deriving amoisture error signal, first actuator means responsive to said moistureerror signal for depositing a layer of dilute stock of controllablethickness on the upper surface of said stock flow in the region of saidaperture to control the moisture content of said sheet approximately tothe moisture target value,

second controller means responsive to said dry weight per unit areameasurement signal and a target value for sheet dry Weight per unit areafor deriving a dry weight error signal, and second actuator meansresponsive to said dry Weight error signal for varying the consistencyof said stock in the region of said aperture to control the fibercontent of said formed sheet so that the sheet has approximately thebone dry basis Weight target value. 33. Control apparatus for a fibrousproduct manufacturing machine including a headbox for storing fibrousstock and having an aperture from which said stock flows onto a movingWire to form a sheet, said apparatus comprising:

gauge means positioned adjacent said formed sheet to provide ameasurement signal indicative of the dry Weight per unit area thereof,

means responsive to said gauge means and a target value for dry Weightper unit area of the sheet to derive 'a dry weight error signal,

actuator means responsive to said dry weight error signal for modulatingthe local flow of said fiber stock to said aperture to provide a sheetof uniform dry weight per unit area equal approximately to the targetvalue,

means for scanning said gauge laterally across said sheet to measure thedry Weight per unit area thereof in each of several discrete zonesacross the width of said web whereby a bone dry basis Weight errorsignal for each of the zones is derived,

said modulating actuator means including:

a plurality of means spaced across the width of said sheet for varyingthe consistency of said stock delivered to said aperture at each of aplurality of cross-sheet regions corresponding to one of said discretecross-sheet zones, and

means responsive to the error signal for each zone for actuating each ofsaid stock consistency varying means according to the measured dryWeight of said scanned zone and a target value for each zone to providea sheet having a uniform dry Weight per unit area.

References Cited UNITED STATES PATENTS 2,928,464 3/1960 Western et al.162-347 2,951,007 8/1960l Lippke 162-259X 3,000,438 9/1961 Alexander162-259 3,092,538 6/1963 Parker 162-216 3,407,114 10/1968 Springuel162-336X 3,413,192 11/1968 Beecher 162-259 3,490,689 1/1970 Hart et al.23S-151.12XR 3,073,153 1/1963 Petitjean 162-263XR OTHER REFERENCES R. W.Ott: The A-B-C System for Moisture and Basis Weight Control in PaperTrade Journal, Mar. 24, 1958, pp. 30-33.

A. L. Petitjean: Non-Destructive Measuring of Drying Profile in MachineDirection in Paper Trade Journal, July 13, 1959, pp. 32-34.

S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner Us.C1. XR.

